Essential Chemistry for Biology: Study Notes

Essential Chemistry for Biology

Introduction: The Role of Chemistry in Biology

Understanding biology requires a solid foundation in chemistry, as all biological processes are rooted in chemical interactions. The study of chemistry helps explain how living organisms function, grow, and interact with their environment.

• Radioactivity can damage DNA and kill cells, but is also used beneficially in medical treatments such as cancer therapy.

• Techniques like PET scans use radioactive substances to visualize diseased tissues in the body.

• Knowledge of chemistry is essential for understanding biological phenomena, from cellular respiration to ecological impacts.

Matter: Elements and Compounds

Basic Concepts of Matter

All living and nonliving things are composed of matter, which is anything that occupies space and has mass. Matter is made up of elements and compounds.

• Element: A substance that cannot be broken down into other substances by chemical reactions.

• Compound: A substance containing two or more elements in a fixed ratio.

• Of the 92 naturally occurring elements, 25 are essential to human life. Four elements—oxygen, carbon, hydrogen, and nitrogen—make up about 96% of the human body.

• Trace elements are required in very small amounts but are essential for life (e.g., iron, iodine).

Atoms and Isotopes

Structure of Atoms

Atoms are the smallest units of matter that retain the properties of an element. Each atom consists of subatomic particles: protons, neutrons, and electrons.

• Proton: Positively charged particle found in the nucleus.

• Neutron: Electrically neutral particle found in the nucleus.

• Electron: Negatively charged particle orbiting the nucleus.

• The atomic number is the number of protons in an atom, unique to each element.

• The mass number is the sum of protons and neutrons in the nucleus.

• Isotopes are atoms of the same element with different numbers of neutrons.

• Radioactive isotopes have unstable nuclei that decay spontaneously, emitting radiation.

Chemical Bonding and Molecules

Types of Chemical Bonds

Chemical bonds form when atoms interact to achieve stable electron configurations. The main types of bonds are ionic, covalent, and hydrogen bonds.

Ionic Bonds

• Formed when one atom transfers electrons to another, resulting in oppositely charged ions that attract each other.

• Ions: Atoms or molecules that have gained or lost electrons and thus have a charge.

• Ionic compounds (e.g., NaCl) are held together by ionic bonds.

Covalent Bonds

• Formed when two atoms share one or more pairs of electrons.

• Covalent bonds are the strongest type of chemical bond and hold atoms together in molecules.

Hydrogen Bonds

• Weak attractions between the slightly positive hydrogen atom of one molecule and the slightly negative atom of another molecule (often oxygen or nitrogen).

• Hydrogen bonds are crucial in water and biological molecules like DNA and proteins.

Chemical Reactions

Nature of Chemical Reactions

Chemical reactions involve the rearrangement of atoms to form new substances. They cannot create or destroy matter, only rearrange it.

• Reactants: Starting materials in a chemical reaction.

• Products: Substances formed as a result of the reaction.

• Example: Cellular respiration and photosynthesis are essential chemical reactions in biology.

Water and Life

Properties of Water

Water is essential for life due to its unique chemical and physical properties, which are largely due to hydrogen bonding.

• Cells are composed of 70–95% water.

• The abundance of water makes Earth habitable.

• Water's polarity and hydrogen bonding explain its life-supporting properties.

Cohesion and Surface Tension

• Cohesion: The tendency of water molecules to stick together due to hydrogen bonding.

• Surface tension: The measure of how difficult it is to break the surface of a liquid; water has high surface tension.

• Cohesion helps transport water in plants from roots to leaves.

Temperature Moderation

• Water resists temperature changes due to hydrogen bonding.

• Heat is absorbed to break hydrogen bonds, and released when bonds form.

• Evaporative cooling: As water evaporates, the surface cools, helping organisms regulate temperature (e.g., sweating).

Ice Floating

• When water freezes, molecules move apart, making ice less dense than liquid water.

• Floating ice insulates bodies of water, allowing life to persist beneath the surface.

Water as a Solvent

• Solution: A homogeneous mixture of two or more substances.

• Solvent: The dissolving agent (e.g., water).

• Solute: The substance dissolved in the solvent.

• When water is the solvent, the solution is called aqueous.

Acids, Bases, and pH

pH Scale and Buffers

The pH scale measures the concentration of hydrogen ions (H+) in a solution, indicating its acidity or basicity.

• Acid: A compound that releases H+ ions into a solution.

• Base: A compound that accepts H+ ions and removes them from solution.

• Buffers: Substances that minimize changes in pH by accepting or donating H+ ions as needed.

Radioactivity and Evolution

Radioactive Isotopes as Evolutionary Clocks

Radioactive decay provides a method for dating fossils and understanding the evolutionary history of life on Earth.

• By measuring the ratio of isotopes in fossils, scientists can estimate their age.

• This technique helps construct the fossil record, a chronological sequence of life on Earth.

Summary Table: Major Elements in the Human Body

Element	Percentage of Body Weight	Role in the Body
Oxygen (O)	65.0%	Component of water and organic molecules; essential for cellular respiration
Carbon (C)	18.5%	Backbone of all organic molecules
Hydrogen (H)	9.5%	Component of water and most organic molecules
Nitrogen (N)	3.3%	Component of proteins and nucleic acids
Calcium (Ca)	1.5%	Bone and teeth structure, muscle function
Phosphorus (P)	1.0%	Component of nucleic acids, ATP, and cell membranes
Trace Elements	<0.01%	Essential for enzyme function and other biological processes